Various types or forms of conduits, such as tubes, columns and linear flow cells are used in analytical instrumentation for transporting and/or processing fluids and samples. For example, chemical analysis instruments that utilize liquid chromatography (LC), high performance liquid chromatography (HPLC), capillary electrophoresis (CE) or capillary electro-chromatography (CEC) perform separation of a sample as the mobile phase containing the sample passes through a separation column, or concentrate a sample in a trap column before delivery of the concentrated sample to a separation column. For example, when a LC system is coupled to a light detector, linear tubes or flow cells are used to contain a fluid for optical analysis. Moreover, when a capillary LC system is interfaced to a mass spectrometer (MS), such as an electrospray ionization mass spectrometer (ESI-MS) instrument, a liquid sample processed by LC is typically pumped through a conduit to an electrospray tip. A high voltage is applied to the tip so that the liquid sample is transformed into charged particles for mass spectroscopic analysis.
Tubing used in analytical apparatus is required to withstand pressures encountered during fabrication and operation. Moreover, the tubing should be reliable for repeated use and have physical and chemical compatibility with process and sample compounds. Generally, tubing material should not corrode or leach, and sample compounds should not adhere to the tubing unless such compounds are required for a separation process.
For high pressure applications, such as HPLC applications, the tubing is typically made from stainless steel or fused silica to provide suitable strength and cleanliness. Fused-silica tubes are commonly used in capillary chromatographic systems due to desirable features. For example, the dimensions of fused silica tubing can be easily controlled during manufacturing. In addition, the wall of fused-silica tubing is clean, non-reactive and smooth, thus providing good transport of small volumes of fluids. A significant disadvantage of fused silica tubing is its vulnerability to fracturing and breaking.
Typically, tubing must be compatible with connectors which provide fluidic connections to various apparatus components. Problems associated with the use of connectors are particularly prominent for high-pressure fabrication and operation, for example, pressures in a range of 10,000 to 18,000 pounds per square inch (psi), as connectors can be the source of fluid leaks. Tubing connections should also minimize void volume, especially for systems having reduced tubing and component dimensions.